This invention relates to an electronic copying system wherein a raster input/scanner (RIS) is used to scan an original document and more particularly, to a diagnostic process for predicting and verifying the performance of the illumination lamp used to incrementally illuminate the document during scan.
Raster input scanners (RIS) systems have become a scanner of choice for electrophotographic and desk top printers. Typically, the RIS comprises a linear or two dimensional array of photosensors mounted in optical alignment with a through lens or a linear leans array. A document is illuminated by a linear light source and a line-by-line scanning function is accomplished by the RIS with the image being detected and stored electronically. Outputs from the photosensor array may be sent to a raster output scanner (ROS) which forms a modulated output pattern on a charged photoreceptor device or belt. Alteratively, the output may be used to drive other image-forming devices such as conventional light lens copiers, ink jet printers and the like or may be sent to a remote location to be stored, for example, in a data processor.
A significant problem with RIS scanners, manifested by degradation of output prints, is variations in the spatial illumination at the image (photosensor) plane. At initial lamp to photosensor calibration, an optimum lamp illumination profile is generated, but this profile changes as the lamp ages, or as the optical system becomes contaminated, causing undesirable variations in the light sensed by the exposed photosites of the photosensor array. Various techniques are known in the prior art for detecting and adjusting for variations in lamp intensity in a scanning system.
U.S. Pat. No. 4,751,377 to Ishizaka et al. discloses a light beam scanning recording apparatus wherein a test pattern is scanned and used to correct a lamp's intensity. (See FIG. 6). U.S. Pat. No. 4,647,981 to Froelich, assigned to Xerox Corporation, discloses an automatic white level control for a RIS wherein a calibration strip is scanned to calibrate a scanner. A closed-loop type circuit is shown which ensures correct calibration. U.S. Pat. No. 3,679,306 to DuBois et al. discloses a feedback system for controlling image light energy wherein a target is imaged and used to control a motor's speed. See Col. 3, lines 29-56. The motor's speed is altered to account for lamp voltage variations, lamp aging and dirty optics. U.S. Pat. No. 4,862,397 to Pryor discloses a remote operation of an optical system wherein a lamp's intensity can be tested and adjusted over a phone line. See Col. 3, lines 13-29. The system has a diagnostic program which detects differences between various components. See Col. 3, line 50-Col. 4 , line 6. U.S. Pat. No. 4,005,940 to Kidd et al., assigned to Xerox Corporation, discloses an optical system alignment apparatus wherein a calibration strip is scanned to test for optical misalignment. Data generated from the calibration strip is used to correct the error. See Col. 7, lines 1-37.
Except for the Froelich patent, the prior art solutions are in the context of a light ones rather than a RIS scanning system. Electronic scanning systems have a greater potential for improving the verification and calibration of the illumination source because of the added intelligence embodied in the electronic circuitry and software associated with detection and process of the scanned image. The present invention is, therefore, directed to a sampling and data display diagnostic technique whereby the illumination and optical output is sequentially sampled by detecting the illumination output reflected from a calibration strip onto a photosensor array. Illumination profile data is accumulated from each sampling and displayed on a video display screen, to provide a visual representative of the illumination and optical spatial profile variations. If the illumination profile variations come within a specified tolerance range, the initial lamp calibration is still valid. If the lamp's output profile is found to exceed this initial specification a recalibration and/or service procedure can be initiated. More particularly, the invention relates to a diagnostic method for visually checking that the scan illumination lamp in a raster input scanner (RIS) is within preset calibration specifications, including the steps of
operating said RIS in a diagnostic mode of operation to scan/illuminate a lamp calibration strip and image the reflected light onto a photosensor array,
converting the output of the photosensor array into video signals representative of the illumination output profile of the lamp, and
displaying the video signals as to provide a visual indication whether the output profile is within said preset calibration specifications and performs these specifications over time.